Error scanning in flash memory

ABSTRACT

Various embodiments include methods, apparatus, and systems to scan at least a portion of a memory device for potential errors when a condition for scanning is met. The condition may be dependent on one or more of a number of read operations, a number of write operations, time, and others. Other embodiments including additional methods, apparatus, and systems are disclosed.

CLAIM OF PRIORITY

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 to U.S. patent application Ser. No. 11/843,466filed on Aug. 22, 2007, which is hereby incorporated by reference hereinin its entirety.

FIELD

Embodiments of this disclosure relate to non-volatile memory devices,including managing information in flash memory devices.

BACKGROUND

Non-volatile memory devices such as flash memory devices are used tostore data or information. Flash memory devices reside in many computersand electronic devices, for example, cellular phones, digital cameras,digital audio players, and digital recorders. Flash memory devices mayalso be used as portable storage devices such as portable UniversalSerial Bus (USB) flash drives or “thumb” drives. In some cases, flashmemory devices may substitute for conventional magnetic hard drives incomputers and other electronic devices or systems.

A flash memory device stores information in numerous memory cells, whichare usually formed in a semiconductor chip. A flash memory deviceusually has a programming or write operation to store information in thecell, a read operation to read information from the cells, and an eraseoperation to erase or delete information from the cells.

In some cases, potential errors may occur in the information stored inthe flash memory device. If the potential errors are left undetected,the information may become unusable. Therefore, there is a need formethods, apparatus, and systems to detect potential errors ininformation in flash memory devices.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a block diagram of a system including a memory deviceaccording to an embodiment of the invention.

FIG. 2 shows a block diagram of a memory device according to anembodiment of the invention.

FIG. 3 is a flow diagram of a method of scanning for errors according toan embodiment of the invention.

FIG. 4 is a chart showing a relationship between error rate and numberof read operations of the memory device of FIG. 2.

FIG. 5 shows a block diagram of a network system according an embodimentof the invention.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of a system 100 according an embodiment ofthe invention. System 100 may reside in an electronic system such as acomputer, a cellular phone, or a digital camera. As shown in FIG. 1,system 100 may include a memory device 101 having a memory array 102with memory cells 104 to store information. The information may includeat least one of data from a user and control data generated by system100. System 100 may also include a memory controller 103 to controlcommunication between memory device 101 and a processor 106 via one ormore interfaces or bus 105 and bus 107.

System 100 may further include a management component 119, which mayparticipate in scanning memory device 101 for potential errors ininformation stored in memory device 101 and correcting the errors. Asdescribed above, undetected potential errors may become unusable. Insystem 100, scanning memory device 101 for potential errors before theinformation becomes unusable and then correcting the errors may reducean overall error rate, or avoid unusable information, or both.

Management component 119 may include monitoring unit 131 to track anumber of accesses to and from memory array by monitoring signals on bus105, 107, or both. For example, monitoring unit 131 may include at leastone counter 151 to count numbers of read operations or write operationsin memory device 101. Management component 119 may also include astorage unit 132 to store one or more values that may be used in errorscanning activities of system 100. Storage unit 132 may include storagecircuit elements such as read only memory (ROM) storage element,electrical erasable programmable ROM (EEPROM), and register circuitry.Management component 119 may also include a time keeper 133, which mayinclude a real-time clock to keep track of time. Management component119 may also include an error correction unit 134 to correct errors thatmay be found in information stored in memory device 101. Errorcorrection unit 134 may include an error correction circuitry to correcterrors based on error correction code (ECC) data associated with thestored information. The ECC data may be generated based on codes such asHamming code, Reed-Solomon code, and BCH code (Bose, Ray-Chaudhuri,Hocquenghem code).

In FIG. 1, arrows 141, 142, and 143 indicate that either the entiremanagement component 119 may reside in only one of memory device 101,memory controller 103, and processor 106, or portions of managementcomponent 119 may be scattered among at least two of memory device 101,memory controller 103, and processor 106. Management component 119 mayinclude software program instructions, firmware, hardware, or acombination thereof. An example of firmware in management component 119includes basic input output system (BIOS) circuitry or circuitry similarto BIOS circuitry of an electronic system. An example of hardware inmanagement component 119 includes circuit elements such as flip-flopcircuitry, register circuitry, state machine circuitry, and othercircuit elements.

Memory device 101 of FIG. 1 may include a non-volatile memory devicesuch as a flash memory device. Processor 106 may include ageneral-purpose processor (e.g., a processor used in a computer) or anapplication specific integrated circuit or ASIC (e.g., a processor usedin a cellular phone or a digital camera). Memory device 101 and memorycontroller 103 may be formed from the same semiconductor die andenclosed in the same semiconductor package or chip. Memory device 101and memory controller 103 may also be formed from separate semiconductordice and enclosed in separate semiconductor packages or separate chips.In some embodiments, memory controller 103 may be omitted, and memorydevice 101 and processor 106 may communicate with each other via one orboth of buses 105 and 107. In some embodiments, memory device 101 mayinclude a memory device of FIG. 2.

FIG. 2 shows a block diagram of a memory device 201 according to anembodiment of the invention. Memory device 201 may include a memoryarray 202 with cells 204 arranged in rows and columns. Row decoder 206and column decoder 208 may respond to an address register 213 and accesscells 204 based on row address and column address signals on lines orterminals 240. Accessing cells 204 may include writing information tocells 204 or reading information from cells 204. A data input/outputcircuit 214 may transfer information between cells 204 and terminals240. Terminals 240 and terminals 241 of memory device 201 may be coupledto an interface or a bus such as bus 105 and 107 of FIG. 1. Terminals240 and 241 may include external terminals of memory device 101 (e.g.,terminals located outside a chip or semiconductor package that containmemory device 101). A read operation may be performed based on readcommand (or signals indicating a read operation) provided on terminal241. A write operation may be performed based on write command (orsignals indicating a write operation) provided on terminals 241. Bymonitoring activity, such as transferring of signals, on terminals 240and 241, memory device 201 may track or determine a number of read andwrite operations performed on the entire memory array 202 or in anindividual block.

A control circuit 216 may control operations of memory device 201 basedon signals on terminals 240 and 241. The operations of memory device 201may include a write operation to write or program information into cells204, a read operation to read information from cells 204, and an eraseoperation to erase information from cells 204. The write, read, anderase operations of memory device 201 may be performed in connectionwith various activities in memory device 201, such as scanning forerrors in information stored in cells 204.

Control circuit 216 may include a management component 219, which mayinclude an embodiment of management component 119 of FIG. 1. In someembodiments, management component 219 of FIG. 2 may include fewercircuit elements than management component 119 of FIG. 1. For example,management component 219 of FIG. 2 may omit an error correction unitsuch as error correction unit 134 of FIG. 1. In FIG. 2, managementcomponent 219 of memory device 201 may participate in scanning cells 204in memory array 202 for potential errors. Management component 219 mayalso participate in correcting the errors.

Memory array 202 may include memory blocks 211 and 212, pages (or rowsof cells) 221, 222, 223, and 224, and sectors 231, 232, 233, 234, 235,236, 237, and 238. As shown in FIG. 2, each of blocks 211 and 212 mayinclude multiple pages, each page may include multiple sectors, and eachsector may include multiple cells. Blocks 211 and 212 may be callederased blocks of a flash memory device. For clarity, FIG. 2 shows anexample of two blocks in memory array 202, two pages in each block, twosectors in each page, and two cells in each sector. In some embodiments,the number of two blocks in memory array 202, the number of pages ineach block, the number of sectors in each page, and the number of cellsin each sector may vary. For example, each of blocks 211 and 212 mayinclude 64 pages. In another example, each of pages 221, 222, 223, and224 in each of blocks 211 and 212 may include four sectors. In anotherexample, each sector in each of blocks 211 and 212 may include 4096cells to store 512 bytes of information.

In FIG. 2, memory device 201 may include a non-volatile memory device.In some embodiments, memory device 201 may include a NAND flash memorydevice where cells 204 may include flash cells arranged in a NAND flashmemory arrangement. In other embodiments, memory device 201 may includea memory device such as a NOR flash memory device, a polymer memorydevice, a ferro-electric random-access memory (FeRAM) device, aphase-change memory (PCM) device, e.g., Ovionics Universal Memory (OUM)device, a nitride read only memory (NROM) device, or a magnetoresistiverandom access memory (MRAM) device.

One skilled in the art will readily recognize that memory device 201 mayinclude other components, which are omitted from FIG. 2 to focus on thevarious embodiments described herein.

Scanning for errors in information stored in memory device 201 may beperformed in device-based, block-based, block-based random page,time-based scanning, or a combination thereof. For example, indevice-based scanning, the entire memory array 202 may be scanned aftera number of sectors in memory array 202 are read or after a number ofread operations are performed on memory device 201. In block-basedscanning, only block 211 or 212 may be scanned after a number of sectorsin the block are read or after a number of read operations are performedon that block. In block-based scanning, only block 211 or 212 may bealso be scanned after a number of sectors in the block are written orafter a number of write operations are performed on that block. Inblock-based random page scanning, a page in a selected one of blocks 211and 212 may be randomly scanned based on a read operation of anotherpage within the same selected block. In time-based scanning, memoryarray 202 may be scanned at after each time interval, for example, ateach number of days.

In some embodiments, the operations and activities in memory device 201,including the scan for errors in information stored in memory device201, may include an embodiment of the activities in FIG. 3.

FIG. 3 is a flow diagram of a method 300 of scanning for errorsaccording to an embodiment of the invention. Method 300 may be used in asystem, such as system 100 of FIG. 1, or in a memory device, such asmemory device 201 of FIG. 2. Thus, the memory device in method 300 mayinclude memory device 101 of FIG. 1 or memory device 201 of FIG. 2.

Activity 310 of FIG. 3 may set a condition to scan for errors ininformation stored in a memory device. A circuit in a controller or aprocessor, such as memory controller 103 or processor 106 of FIG. 1, ora circuit, such as control circuit 216 of memory device 201 of FIG. 2,may set the condition. Setting the condition may include storing atleast one of selected values in a storage unit. A storage unit, such asstorage unit 132 of FIG. 1, may store the selected values set byactivity 310.

Setting the condition in activity 310 may include storing a firstselected value such that scanning for errors may be performed when anumber of read operations in the memory device exceeds or is at leastequal to the first selected value. For example, when the first selectedvalue is set at M, where M is an integer, scanning for errors may beperformed when the number of read operations the memory device exceedsor is at least equal to M.

Setting the condition in activity 310 may also include storing a secondselected value such that scanning for errors may be performed when anumber of read operations in a block of the memory device exceeds or isat least equal to the second selected value. For example, when thesecond selected value is set at B, where B is an integer, scanning forerrors may be performed when the number of read operations in the blockexceeds or is at least equal to B.

Setting the condition in activity 310 may also include storing a thirdselected value such that scanning for errors may be performed at arandom location in a block of the memory device when a number of readoperations in a block of the memory device exceeds or is at least equalto the third selected value. For example, when the third selected valueis set at R, where R is an integer, scanning for errors may be performedat the random location when the number of read operations in the blockexceeds or is at least equal to R.

Setting the condition in activity 310 may also include storing a fourthselected value such that scanning for errors may be performed in a blockof the memory device when a number of write operations in that blockexceeds or is at least equal to the fourth selected value. For example,when the fourth selected value is set at W, where W is an integer,scanning for errors may be performed on the block when the number ofwrite operations in the block exceeds or is at least equal to W.

Setting the condition in activity 310 may also include storing a fifthselected value such that scanning for errors may be performed at everytime interval that is indicated by the fifth value. For example, whenthe fifth selected value is set at T, which may represent a timeinterval such as a number of days, scanning for errors may be performedat every time interval indicated by T.

In activity 310, the first, second, third, fourth, and fifth selectedvalues may be stored in any combination. For example, only one of thefirst, second, third, fourth, and fifth selected values may be stored.Thus, the condition to scan for errors in information in the memorydevice may depend on only one of the first, second, third, fourth, andfifth selected values stored by activity 310. In another example, atleast two of the first, second, third, fourth, and fifth selected valuesmay be stored. Thus, the condition to scan for errors in information inthe memory device may depend on at least two of the first, second,third, fourth, and fifth selected values.

Activity 320 may access the memory device. Accessing the memory devicemay include performing a write operation to store or write informationto the memory device, and performing a read operation to readinformation from the memory device.

Activity 330 may track a number of accesses. The number of accesses mayinclude a number of accesses to and from the memory device. In someembodiments, activity 330 may track the number of accesses by countingthe number of accesses. A counter, such as counter 151 of FIG. 1, maycount the number of accesses in activity 330. The counter, or a storageunit such as storage unit 132 of FIG. 1, may store the number ofaccesses after they are counted.

The number of accesses may include a number of read operations in thememory device. The number of read operations may include a total numberof read operations performed on sectors of more than one block of thememory device. The number of accesses may also include a number of readoperations in a block of the memory device. The number of accesses mayalso include a number of write operations in a block of the memorydevice.

Activity 340 determines whether condition to scan for errors is met. Inactivity 340, the number of accesses in activity 330 may be comparedwith a corresponding selected value set by activity 310. The result ofthe comparison may determine whether the condition is met.

For example, the condition in activity 340 is met when a number of readoperations in the memory device exceeds or is at least equal to aselected value (e.g., value B described above), which may be stored in astorage device by activity 310.

In another example, the condition in activity 340 is met when a numberof read operations in a block of the memory device exceeds or is atleast equal to a selected value (e.g., value B described above), whichmay be stored in a storage device by activity 310.

In another example, the condition in activity 340 is met when a numberof read operations in a block of the memory device exceeds or is atleast equal to a selected value (e.g., value R described above), whichmay be stored in a storage device by activity 310.

In another example, the condition in activity 340 is met when a numberof write operations in a block of the memory device exceeds or is atleast equal to a selected value (e.g., value W described above), whichmay be stored in a storage device by activity 310.

In another example, the condition in activity 340 is met when an amountof time has passed after the information was stored in the memorydevice, and the amount of time exceeds or is at least equal to an amountof time indicated by a selected value, which may be set in activity 310.

As shown in FIG. 3, when the condition in activity 340 method 300 is notmet (indicated by “NO”), method 300 may repeat activity 330. Method 300may continue with activity 350 when the condition is met (indicated by“YES”).

Activity 350 may scan for errors. Scanning in activity 350 may includescanning only a portion of the memory device or the entire memorydevice. Scanning in activity 350 may include at least one ofdevice-based scanning, block-based scanning, block-based random locationscanning, and time-based scanning.

Activity 350 may perform device-based scanning when the number of readoperations in the memory device exceeds or is at least equal to aselected value (e.g., value M described above). In device-basedscanning, activity 350 may read cells that have stored information andskip reading cells that have no stored information. The cells havingstored information may reside in one or more blocks of the memorydevice. In some embodiments, in device-based scanning, scanning inactivity 350 may read both cells with stored information and cellswithout stored information.

Activity 350 may perform block-based scanning when the number of readoperations in a block exceeds or is at least equal to a selected value(e.g., value B described above). In block-based scanning, activity 350may read cells in only a selected block when the number of readoperations in the selected block exceeds or is at least equal to thesecond selected value stored by activity 310.

Activity 350 may perform block-based random location scanning when thenumber of read operations in a block exceeds or is at least equal to aselected value (e.g., value R described above). In block-based randomlocation scanning, activity 350 may read cells at a random location in ablock to scan for errors. The rate at which activity 350 may read thecells at a random location may be based on a selected value such thevalue R. In some embodiments, the address of the random location may bea function of an offset value and an address provided to the memorydevice during a normal memory read operation (not scanning for errorsread operation). For example, if a selected value, such as R, is 12 andthe offset value is 16, then after every 12 normal memory readoperations are performed to a block, an additional read operation (e.g.,the 13th read operation) may be performed to read cells at a randomlocation to scan for errors. In this example, the address for the randomlocation in the additional read operation (13th read operation) may bedetermined based on the address of the location in the 12th readoperation and the offset value (which is 16 in this example). Forexample, the address of the random location in the 13th read operationmay be determined from the address of the location in the 12th readoperation plus (or minus) the offset value. The offset value may beselected and stored in a storage unit, such as the storage unit used inactivity 310. In block-based random location scanning, the offset valuemay be obtained by accessing the storage unit where the offset value maybe stored.

In some embodiments, the random location may include a location of apage of a block. Thus, in some embodiments, the offset value may beselected based on a number of pages in a block. For example, when ablock has 64 pages numbering from 0 to 63, the offset value may be from1 to 62. In this example, the address of the random page (to be scannedfor errors) may be the address of the page (one of the 64 pages) beingread in the normal read operation plus (or minus) the offset value suchthat the address of the random page may be within the block.

Scanning in activity 350 may also perform block-based scanning when thenumber of write operations in a block exceeds or is at least equal to aselected value (e.g., value W described above), which may be stored byactivity 310. For example, activity 350 may read cells at one locationin a block to scan for errors after writing information to cells atanother location of the same block.

As described in FIG. 2, a block may include multiple pages. The blockmay be written page by page at different write operations and in asequential order, for example in a sequential order of a first page,intermediate pages, and a last page. Since the block may be written pageby page, the number of operations may correspond to the number of pagesthat have been written. In FIG. 3, activity 350 may read cells of thepages that have been written after writing information to a new page.For example, if a selected value is 14 (e.g., W=14) and if a number ofwrite operations has been performed on a block is 14 (e.g., 14 pageshave been written), then, after writing to the block in the 15th writeoperation, activity 350 may read cells that are previously written(e.g., cells from the first page to the 14th page) to scan for errors.In some embodiments, using the same example herein, activity 350 mayread cells from the entire block (including cells written in the 15thwrite operation) to scan for errors after the 15th write operation.

In some embodiments, the selected value may be chosen such that activity350 may reads cells from every page of a block to scan for errors everytime after cells from a page of the block is written. For example, theselected value may be set at one (e.g., W=1). In other embodiments, toscan for errors, the selected value may be chosen such that activity 350may reads cells from pages of a block only after at least one-half of anumber of pages of block is written. For example, the selected value maybe set at one one-half number of the pages of the block (e.g., W=(½) P,where P is the number of the pages of the block).

Activity 350 may perform time-based scanning at time interval to scanfor errors. In time-based scanning, activity 350 may read cells thathave stored information to scan for errors. For example, if a selectedvalue is 30 days (e.g., T corresponds to a value to 30 days), then every30 days, activity 350 may read cells that have stored information toscan for errors.

As described above in activity 350, information may be read from thecells of the memory device to scan for errors based on one or morecondition being met. A correction operation may be performed to correctany errors in the information based on the scan that is obtained fromactivity 350.

In some embodiments, scanning for errors in activity 350 may includereading information from memory cells of the device and determining ECCdata (e.g., new check bits) associated with the information when theinformation is read from the cells. Then, the ECC data (e.g., new checkbits) may be compared with the ECC data (e.g., old check bits)associated with the information when the information was written intothe memory cells. A mismatch between the two ECC data (e.g., old and newcheck bits) may indicate an occurrence of errors in the information.

In other embodiments, scanning for errors in activity 350 may includeaccessing specialized hardware in the memory device to determine iferrors in information may occur. For example, scanning for errors inactivity 350 may include accessing reference cells of the device todetermine if voltage level values representing the information inreference cells remain within a limit. In this example, the errors ininformation may occur if the voltage level values are outside the limit(e.g., the voltage level values dropping below the limit or exceedingthe limit). In some embodiments, the reference cells may be a portion ofcells a of memory array such as cells 104 of memory array 102 of FIG. 2.In some embodiments, a controller or a processor, such as memorycontroller 103 or processor 106 of FIG. 1 (instead of an errorcorrection such as error correction unit 134 of FIG. 1) may accessspecialized hardware (e.g., reference cells) in the memory device todetermine if errors in information occur.

Activity 360 may correct an error if one is found. For example, activity360 may check the information to determine a bit error quantity (one ormore error bits that may occur) when an error in the information exists.Activity 360 may then correct the error when the bit error quantity isequal to or greater than to a selected value. A correction unit, such aserror correction unit 134 of FIG. 1, may perform the correction. In someembodiments, the correction unit may correct the error when the biterror quantity is at least one. Thus, in these embodiments, any errorbit found may be corrected. In other embodiments, the correction unitmay correct the error only when the bit error quantity exceeds somevalue for each number of bits scanned. The number of bits scanned may bethe number of bits in a sector. For example, the correction unit maycorrect the error only when the bit error quantity exceeds three foreach number of bits in a sector that is scanned.

Activity 370 may update tracking information. For example, one or morevalues that is tracked in activity 330 may be reset to an initial valueafter a scan for errors in activity 350 is performed. For example, aftera block is scanned for errors, the number of read operations performedon that block may be reset to the initial value (e.g., zero) so thatanother scan for errors may be performed to the block when the number ofread operations performed on that block, after reset, is least equal tothe selected value (e.g., value B). Other values that are tracked byactivity 330 may be reset after a scan for errors based on the othervalues are performed. After activity 370, method 300 may repeat one ormore other activities described above. For example, method 300 mayrepeat the other activities, described above, starting from activity320.

The individual activities of method 300 may not have to be performed inthe order shown or in any particular order. Some activities may berepeated, and others may occur only once. Various embodiments may havemore or fewer activities than those shown in FIG. 3. For example, method300 may omit one or more of activities 320, 330, and 370 when method 300performs time-based scanning. In some embodiments, method 300 mayinclude the activities or operations described with reference to FIG. 1through FIG. 2 above and FIG. 4 and FIG. 6 below.

FIG. 4 is a chart showing a relationship between error rate and numberof read operations of memory device 201 of FIG. 2. In FIG. 4, X and Nmay represent some particular numbers of read operations performed onmemory device 201. R1, R2, and R3 in FIG. 4 may represent error rates inrelation to the number of read operations. As shown in FIG. 4, the errorrate may increase in a linear fashion from R1 to R2 when the number ofread operations is less than or equal to X. When the number of readoperations is more than X, the error rate may increase in an exponentialfashion from R2 to R3. Thus, in FIG. 4, the error rate increases at arelatively higher rate when the number of read operations is at least X.Therefore, in memory device 201, scanning for errors when the number ofthe read operations is at least X may be more economical than scanningfor errors when the number of the read operations is less than X,because the chance of finding errors may be significantly greater whenthe number of read operations is X or more.

In some embodiments, a number of read operations such as X in FIG. 4 maybe determined during a test. For example, during a test, numerous readoperations may be performed on memory device 201, then error rates(e.g., R1, R2, and R3) corresponding to the read operations may berecorded. The number of read operations, such as X in FIG. 4, may bedetermined at a point where the error rate starts to show a significantchange. For example, as shown in FIG. 4, X may be determined at a pointcorresponding to R2 because the curve connecting R1, R2 and R3 shows asignificant change in the slope between R2 and R3 relative to the slopebetween R1 and R2. In some embodiments, the number of read operations Xis about 1000. In some embodiments, the number of read operations X isin a range of about 1000 to about 2000. Thus, in some embodiments,scanning for errors in information stored in a memory device, such asmemory device 201, may start when the number of read operations (e.g.,X) is at least 1000.

FIG. 5 shows a network 500 according to an embodiment of the invention.Network 500 may include systems 561 and 562 communicating with eachother via a connection 563. Connection 563 may include a wired orwireless connection. In some embodiments, connection 563 may include aninterne connection.

System 561 may include a processor 510, an image sensor device 520, amemory device 525, a memory controller 530, a graphics controller 540, acircuit module 545, an input and output (I/O) controller 550, a display552, a keyboard 554, a pointing device 556, peripheral device 558, and abus 560 to transfer information among the components of system 561.System 561 may also include an antenna 570 to transmit and receiveinformation wirelessly. System 561 may also include a circuit board 502on which some components of system 561 may be located. In someembodiments, the number of components of system 561 may vary. Forexample, in some embodiments, system 561 may omit one or more of display552, image sensor device 520, memory device 525, and circuit module 545.System 561 may include an embodiment of system 100 of FIG. 1.

Processor 510 may include a general-purpose processor, e.g., a processorused in a computer. Processor 510 may include an application specificintegrated circuit (ASIC), e.g., a processor used in a cellular phone,or a digital camera or camcorder. Processor 510 may include a singlecore processor or a multiple-core processor. Processor 510 may executeone or more programming commands to process information and produceprocessed information. The information that is processed by processor510 may include digital output information provided by other componentsof system 561, such as by image sensor device 520 or memory device 525.

Image sensor device 520 may include a complementarymetal-oxide-semiconductor (CMOS) image sensor having a CMOS pixel arrayor charge-coupled device (CCD) image sensor having a CCD pixel array.

Memory device 525 may include a volatile memory device, a non-volatilememory device, or a combination of both. For example, memory device 525may include a dynamic random access memory (DRAM) device, a staticrandom access memory (SRAM) device, a flash memory device such as NANDor NOR flash memory device, or a combination of DRAM, SRAM, and flashmemory devices. In some embodiments, memory device 525 may include oneor more embodiments of memory device 101 or 201 described above withreference to FIG. 1 through FIG. 4.

Display 552 may include an analog display or a digital display. Display552 may include a liquid crystal display (LCD), or a plasma display.Display 552 may receive information from other components. For example,display 552 may receive information that is processed by one or more ofimage sensor device 520, memory device 525, graphics controller 540, andprocessor 510 to display information including text and images.

Circuit module 545 may include a circuit module of a vehicle. Circuitmodule 545 may receive information from other components to activate oneor more subsystem of the vehicle. For example, circuit module 545 mayreceive information that is processed by one or more of image sensordevice 520, memory device 525, and processor 510, to activate one ormore of an air bag system of a vehicle, a vehicle security alarm, andobstacle alert system in a vehicle.

As shown in FIG. 500, system 561 may include a machine-readable medium571. System 562 may include a machine-readable medium 572. Each ofmachine-readable media 571 and 572 may include a memory, e.g., removablestorage media, and any memory including an electrical, optical, orelectromagnetic conductor.

Each of machine-readable media 571 and 572 may contain thereonassociated information (e.g., computer or software program instructionsand/or data), which when executed, results in a machine (e.g.,components of system 561) performing one or more of the activitiesdescribed herein with respect to the FIG. 1 through FIG. 5.

Upon reading and comprehending the content of this disclosure, one ofordinary skill in the art will understand the manner in which a softwareprogram can be launched from a computer-readable medium in acomputer-based system to execute the functions defined in the softwareprogram. One of ordinary skill in the art will further understand thevarious programming languages that may be employed to create one or moresoftware programs designed to implement and perform the methodsincluding the activities described herein. The programs may bestructured in an object-orientated format using an object-orientedlanguage such as Java or C++. Alternatively, the programs can bestructured in a procedure-orientated format using a procedural language,such as assembly or C. The software components may communicate using anyof a number of mechanisms well known to those skilled in the art, suchas application program interfaces or interprocess communicationtechniques, including remote procedure calls. The teachings of variousembodiments are not limited to any particular programming language orenvironment.

The illustrations of systems and apparatus herein, such as systems 100,561, and 562, and memory devices 201, and 525 are intended to provide ageneral understanding of the structure of various embodiments, and notas a complete description of all the elements and features of apparatusand systems that might make use of the structures described herein.

The novel apparatus, systems, and method of various embodiments mayinclude, be included, or used in electronic circuitry used in high-speedcomputers, communication and signal processing circuitry, single ormulti-processor modules, single or multiple embedded processors,multi-core processors, data switches, and application-specific modulesincluding multilayer, multi-chip modules. Such apparatus and systems mayfurther be included as sub-components within a variety of electronicsystems, such as televisions, cellular telephones, personal computers(e.g., laptop computers, desktop computers, handheld computers, tabletcomputers, etc.), workstations, radios, video players, audio players(e.g., MP3 (Motion Picture Experts Group, Audio Layer 3) players),vehicles, medical devices (e.g., heart monitor, blood pressure monitor,etc.), set top boxes, and others.

The above description and the drawings illustrate some embodiments ofthe invention to enable those skilled in the art to practice theembodiments of the invention. Other embodiments may incorporatestructural, logical, electrical, process, and other changes. In thedrawings, like features or like numerals describe substantially similarfeatures throughout the several views. Examples merely typify possiblevariations. Portions and features of some embodiments may be includedin, or substituted for, those of others. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. Therefore, the scope of various embodiments of theinvention is determined by the appended claims, along with the fullrange of equivalents to which such claims are entitled.

The Abstract is provided to comply with 37 C.F.R. §1.72(b) requiring anabstract that will allow the reader to quickly ascertain the nature andgist of the technical disclosure. The Abstract is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims.

1. An apparatus comprising: a circuit to set at least one condition toscan for errors in information stored in a memory device, the conditionto scan being based on a number of accesses to cells of the memorydevice, wherein the condition to scan is stored in the memory device;and a component to scan for errors in the information when the conditionis met.
 2. The apparatus of claim 1, wherein the condition for scanningis further based on an amount of time passed after the information wasstored in the memory device.
 3. The apparatus of claim 1, wherein thecondition is met when a number of accesses to cells of the memory deviceis at least equal to a selected value.
 4. The apparatus of claim 2,wherein the number of accesses comprises a number of read operations. 5.The apparatus of claim 2, wherein the number of accesses comprises anumber of write operations.
 6. The apparatus of claim 1, furthercomprising a storage unit to store a selected value, wherein thecondition is met when a number of read operations performed on only aselected portion of the memory device is at least equal to the selectedvalue.
 7. The apparatus of claim 1, further comprising a storage unit tostore a selected value, wherein the condition is met when a number ofwrite operations performed on only a selected portion of the memorydevice is at least equal to the selected value.
 8. An apparatuscomprising: a component to scan for errors in information stored in amemory device when a condition for scanning is met, the condition forscanning being based on an amount of time passed after the informationwas stored in the memory device, wherein the condition to scan is storedin the memory device.
 9. The apparatus of claim 8, wherein the componentcomprises a storage unit to store a selected value, wherein thecondition is met when the amount of time is at least equal to theselected value.
 10. The apparatus of claim 8, wherein the componentcomprises a storage unit to store an offset value, wherein the componentis to scan for errors at a location with an address based on the offsetvalue.
 11. The apparatus of claim 8, wherein the component comprises areal-time clock to determine a time interval to scan for errors.
 12. Amethod comprising: scanning for errors in information stored in a memorydevice when a condition for scanning is met, the condition for scanningis being based on a number of accesses to cells of the memory device,wherein the condition to scan is stored in the memory device.
 13. Themethod of claim 12, further comprising: counting a number of readoperations in the memory device to determine whether the condition forscanning is met.
 14. The method of claim 12, further comprising;counting a number of write operations in the memory device to determinewhether the condition for scanning is met.
 15. The method of claim 12,further comprising: comparing error correction code (ECC) dataassociated with the information when the information is read with ECCdata associated with the information when the information was writteninto the cells to determine whether an error occurs.
 16. The method ofclaim 15, further comprising: correcting at least one error bit in theinformation when the error occurs.
 17. The method of claim 12, whereinthe scanning is performed when the number of accesses is at least 1000.18. A method comprising: scanning for errors in information stored in amemory device when a condition for scanning is met, the condition forscanning being based on an amount of time passed after the informationwas stored in the memory device, wherein the condition to scan is storedin the memory device.
 19. The method of claim 18, wherein the conditionfor scanning is met when the amount of time is at least one day.
 20. Themethod of claim 18, wherein scanning is performed at a selected timeinterval.